1. Field of the Invention
The present invention relates generally to a technique for recovering blast furnace gas. More particularly, the invention relates to a system for recovering blast furnace gas, which includes dry type dust removal equipment. Further particularly, the invention relates to a cooling system for the blast furnace gas.
2. Description of the Background Art
In the modern blast furnace, blast furnace gas is collected or recovered for utilizing in generation of electric power and so forth. In the blast furnace gas path, a dust removal equipment, such as bag filter, is provided for removing dust carried with the blast furnace gas. In recent years, dry type dust-removal equipments have been preferred because of higher temperature gas can be circulated to an electric power generation facility for better power generation performance.
Such blast furnace gas recovery system is effective for higher power generation performance in the normal operation state of the blast furnace, in which temperature of blast furnace gas is held stable at about 200.degree. C. However, when channeling for forming direct path for furnace gas and whereby directly discharging higher temperature gas through top of the furnace, the blast furnace gas temperature rapidly rises to about 300.degree. C. to about 400.degree. C. and, in the worst case, to about 800.degree. C. Such high temperature may cause damage in the dust-removal equipment, a turbine in a power generator, a septum valve and other component in the blast furnace gas recovery system. For preventing the components in the system from being damaged, the gas has to be cooled to lower the temperature in a level lower than critical temperature of respective components.
For example, Japanese Patent First (unexamined) Publication (Tokkai) Showa 54-40207, Japanese Patent First Publication (Tokkai) Showa 54-81107 and Japanese Patent First Publication (Tokkai) Showa 57-43913 propose cooling of gas by spraying water in dust catchers. These proposal is effective for lowering the gas temperature. However, in such case, the water spraying arrangement has to have a cooling capacity to satisfactorily lower the gas temperature even when channeling occurs. This increases cost for providing the water spraying arrangement. Since channeling of the furnace rarely occur and therefore, the aforementioned facility is only for emergency case, substantial cost increase is normally unacceptable.
On the other hand, the critical temperature of each component of the blast furnace gas recovery system is differentiated to others. For instance, the critical temperature of the bag filter as the dust-removal equipment is normally about 250.degree. C., the critical temperature of the turbine is normally about 200.degree. C., and the critical temperature of the septum valve is normally about 100.degree. C. or lower. This means that the gas temperature at the bag filter is to be controlled at about 250.degree. C. or lower and is not necessary to be lower than the critical temperature of the turbine and the septum valve.